Alma Observations of Massive Molecular Gas Filaments Encasing Radio Bubbles in the Phoenix Cluster

DRAFT VERSION DECEMBER 16, 2016 Preprint typeset using LATEX style AASTeX6 v. 1.0 ALMA OBSERVATIONS OF MASSIVE MOLECULAR GAS FILAMENTS ENCASING RADIO BUBBLES IN THE PHOENIX CLUSTER H. R. RUSSELL1∗, M. MCDONALD2, B. R. MCNAMARA3;4, A. C. FABIAN1, P. E. J. NULSEN5;6, M. B. BAYLISS2;7, B. A. BENSON8;9;10, M. BRODWIN11, J. E. CARLSTROM10;9, A. C. EDGE12, J. HLAVACEK-LARRONDO13, D. P. MARRONE14, C. L. REICHARDT15 AND J. D. VIEIRA16 1 Institute of Astronomy, Madingley Road, Cambridge CB3 0HA 2 Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA 3 Department of Physics and Astronomy, University of Waterloo, Waterloo, ON N2L 3G1, Canada 4 Perimeter Institute for Theoretical Physics, Waterloo, ON N2L 2Y5, Canada 5Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA 6ICRAR, University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia 7Department of Physics and Astronomy, Colby College, 5100 Mayflower Hill Dr, Waterville, ME 04901, USA 8Fermi National Accelerator Laboratory, Batavia, IL 60510-0500, USA 9Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637, USA 10Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA 11Department of Physics and Astronomy, University of Missouri, Kansas City, MO 64110, USA 12Department of Physics, Durham University, Durham DH1 3LE 13Département de Physique, Université de Montréal, Montréal, QC H3C 3J7, Canada 14Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA 15School of Physics, University of Melbourne, Parkville VIC 3010, Australia 16Department of Astronomy and Department of Physics, University of Illinois, 1002 West Green St., Urbana, IL 61801, USA ABSTRACT 10 We report new ALMA observations of the CO(3-2) line emission from the 2:1 ± 0:3 × 10 M molecular gas reservoir in the central galaxy of the Phoenix cluster. The cold molecular gas is fuelling a vigorous starburst at a -1 rate of 500-800M yr and powerful black hole activity in the form of both intense quasar radiation and radio jets. The radio jets have inflated huge bubbles filled with relativistic plasma into the hot, X-ray atmospheres surrounding the host galaxy. The ALMA observations show that extended filaments of molecular gas, each 10 - 20 kpc long with a mass of several billion solar masses, are located along the peripheries of the radio bubbles. The smooth velocity gradients and narrow line widths along each filament reveal massive, ordered molecular gas flows around each bubble, which are inconsistent with gravitational free-fall. The molecular clouds have been lifted directly by the radio bubbles, or formed via thermal instabilities induced in low entropy gas lifted in the updraft of the bubbles. These new data provide compelling evidence for close coupling between the radio bubbles and the cold gas, which is essential to explain the self-regulation of feedback. The very feedback mechanism that heats hot atmospheres and suppresses star formation may also paradoxically stimulate production of the cold gas required to sustain feedback in massive galaxies. Keywords: cooling flows — galaxies:active — galaxies: clusters: Phoenix — radio lines: galaxies 1. INTRODUCTION galaxies and central cluster galaxies have also revealed huge arXiv:1611.00017v2 [astro-ph.GA] 15 Dec 2016 The energy output by active galactic nuclei (AGN) has cavities where the hot gas has been displaced by expanding long been recognized as sufficient to unbind the interstel- radio bubbles inflated by radio jets (McNamara et al. 2000; lar medium from even the most massive host galaxies (Silk Fabian et al. 2000, 2006). Known as AGN feedback, these & Rees 1998). Recent observations of ionized and molecu- energetic outbursts are therefore observed to couple effec- lar gas outflows driven by intense radiation or radio jet ac- tively to the cold and warm interstellar gas and the hot gas tivity from the central AGN show that this energy can be atmospheres surrounding massive galaxies. AGN feedback efficiently coupled to the surrounding interstellar gas (eg. is an essential mechanism in galaxy formation that powers Morganti et al. 2005; Nesvadba et al. 2006; Feruglio et al. gas outflows to truncate massive galaxy growth. This pro- 2010; Rupke & Veilleux 2011; Alatalo et al. 2011; Dasyra cess is thought to produce the observed evolution of galaxies & Combes 2011; Morganti et al. 2015). Chandra X-ray ob- from gas-rich, star forming systems to ‘red and dead’ ellipti- servations of the hot atmospheres surrounding giant elliptical cals and imprint the observed coevolution of massive galax- 2 ies and supermassive black holes (SMBHs; Magorrian et al. ture AGN activity. 1998; Croton et al. 2006; Bower et al. 2006). Here we present new ALMA observations of the CO(3- However, the details of how a SMBH can regulate the 2) emission from the molecular gas in the central galaxy growth of its host environment over many orders of magni- of the Phoenix cluster. Discovered with the South Pole tude in spatial scale are still poorly understood. In the most Telescope, the Phoenix cluster (SPT-CLJ2344-4243), at red- massive galaxies at the centres of cool core galaxy clusters, shift z = 0:596, is the most luminous X-ray cluster known the radiative cooling time of the hot gas atmosphere can fall (Williamson et al. 2011; McDonald et al. 2012), and the -1 below a Gyr and heat input from the AGN must be distributed 500 - 800M yr starburst hosted by its central galaxy is throughout the central 100 kpc to prevent the formation of a amongst the largest found in any galaxy below redshift 1. cooling flow (eg. Edge et al. 1992; Peres et al. 1998; Voigt The star formation is observed in bright filaments stretch- & Fabian 2004). Without this energy input, gas would cool ing beyond 100 kpc, sustained by a 20 billion solar mass unimpeded from the cluster atmosphere and produce at least reservoir of molecular gas (McDonald et al. 2013a, 2014). 12 an order of magnitude more molecular gas and star formation The stellar mass of the massive central galaxy is 3×10 M than is observed in central cluster galaxies (Johnstone et al. (McDonald et al. 2012, 2013a) and it hosts an unusual cen- 1987; Edge 2001; Salomé & Combes 2003). Radio jets pow- tral supermassive black hole that is powering both intense ered by the central AGN inflate buoyant radio bubbles and radiation and relativistic jets. Observations show these to be drive shocks and sound waves into the intracluster medium distinct modes of AGN feedback. The black hole may be to produce distributed heating throughout the cluster core (for in the process of transitioning from a radiatively powerful reviews see McNamara & Nulsen 2007, 2012; Fabian 2012). quasar to a radio galaxy (eg. Churazov et al. 2005; Russell X-ray studies of large samples of galaxy groups and clusters et al. 2013; Hlavacek-Larrondo et al. 2013) whose mechani- show that this energy input is sufficient to replace the major- cal power output of ∼ 1046 erg s-1 is among the largest mea- ity of the radiative losses from the cluster gas on large scales sured (eg. Hlavacek-Larrondo et al. 2015; McDonald et al. (Bîrzan et al. 2004; Dunn & Fabian 2006; Rafferty et al. 2015). The Phoenix cluster therefore hosts an extreme exam- 2006). The heating rate supplied by the AGN is also observed ple of this common mechanism in galaxy evolution. Both the to be closely correlated with the cooling rate of the cluster powerful black hole activity and the vigorous starburst are atmosphere, which implies a highly effective feedback loop fuelled by the massive cold molecular gas reservoir, whose operating over this huge range of spatial scales. A few per structure can now be resolved with ALMA to understand how cent of the most rapidly cooling cluster gas does cool to low these processes are regulated. temperatures and likely feeds the observed cold molecular We assume a standard ΛCDM cosmology with H0 = -1 -1 gas reservoirs and star formation in the central galaxy. Al- 70 km s Mpc , ΩM = 0:27 and ΩΛ = 0:73. At the redshift though the level of gas cooling falls far below the predictions of the Phoenix cluster z = 0:596 (Ruel et al. 2014; McDonald of cooling flows, prompt accretion of this residual compo- et al. 2015), 1 arcsec corresponds to 6:75 kpc. nent is likely required to link the large scale cooling rate to the energy output of the AGN in an efficient feedback loop. 2. DATA REDUCTION Observations of ionized and molecular gas at the centres of The brightest cluster galaxy (BCG) in the Phoenix cluster clusters have revealed cool gas filaments extending radially was observed by ALMA on 15 and 16 June 2014 (Cycle 2, from the galaxy centre towards radio bubbles inflated by the ID 2013.1.01302.S; PI McDonald) simultaneously covering jet (Fabian et al. 2003; Salomé et al. 2006, 2008; Hatch et al. the CO(3-2) line at 216:66 GHz and the sub-mm continuum 2006; Lim et al. 2008). In the Perseus cluster, the velocity emission in three additional basebands at 219.5, 230.5 and structure of the Hα-emitting filaments, which are coincident 232:5 GHz. The single pointing observations were centred with detections of CO emission from the IRAM 30 m tele- on the nucleus with a field of view of 28:5 arcsec. The total scope, traces streamlines underneath a buoyantly rising radio time on source was 58:5min split into nine ∼ 6min obser- bubble (Salomé et al. 2006, 2011). ALMA observations of vations and interspersed with observations of the phase cali- molecular gas at the centres of clusters (Russell et al.

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